1. Field of the Invention
The present invention relates to injection molding machines and, more particularly, to the die closing unit of an injection molding machine and to adjustable roller track supporting means for the movable die carrier member of such a die closing unit.
2. Description of the Prior Art
In most injection molding machines, especially heavyduty machines, the movable die carrier member is guided for horizontal die opening and closing movements by means of two or four horizontal tie rods. Under the weight of die carrier member, the guide bushings tend to develop frictional heat and wear, with the result that the dimensional accuracy of the injection-molded parts declines. Replacement of the bushings is time consuming and costly, because it must be done by the manufacturer.
It has therefore already been suggested to relieve the tie rods of their load-carrying function with the aid of exterior guide elements which support the movable die carrier frame directly on the machine base, or on a cantilever-type guide frame which is attached to the machine base. These load-carrying exterior guide elements may be of the sliding or rolling type.
A rolling guide support on a cantilever frame is disclosed in German Pat. No. 21 37 284 and corresponding U.S. Pat. No. 3,841,823. Two guide rollers support the movable die carrier member on a pair of guide rails, and guide flanges on the rollers provide a certain lateral guidance.
Success in relieving the tie rods of their load-carrying function requires not only a high degree of manufacturing precision, but also considerable assembly skill. It has therefore also been suggested to provide vertical and, where necessary, horizontal adjustability in conjunction with the exterior guide elements. Vertical adjustability is suggested in the German Offenlegungsschrift (Publ. Application) No. 29 43 118 for a supporting roller, and in the German Offenlegungsschrift No. 30 06 230 for a supporting slide shoe. Vertical and horizontal adjustability is suggested in the German Offenlegungsschrift No. 30 29 597 and the corresponding U.S. Pat. No. 4,315,728, in connection with an angled slide shoe riding on horizontal and vertical faces of a guide rail.
The known adjustable exterior guide assemblies require a rigid connection between the die carrier member and the adjustable guide roller brackets or slide shoes, in order to prevent the latter from canting on the guide rails. Guide rollers have the obvious disadvantage of providing only line contact on the rails, thus having only a limited load-carrying capability.
For very heavy die carriers, it has therefore become necessary to resort to slide shoes with special synthetic lowfriction bearing plates, in order to reduce the specific contact pressure on the bearing surfaces. These slide shoes, however, have the shortcoming of creating a much higher frictional resistance than rollers and of generating a correspondingly high heat buildup which is detrimental to the life of the bearing surfaces. The higher frictional resistance also means a corresponding increase in the energy consumption of the hydraulic drive of the die closing unit.
It is also known, on the other hand, that comparatively high loads can be transmitted under rolling friction to a flat runway by means of a roller track assembly which uses an endless row of recirculating journal-free bearing rollers which pass between the runway and a parallel opposing face of a track core. The bearing rollers are laterally guided between the flanks of their track core and spaced apart in the sense of advance by means of spacer elements. Head pieces bolted to both ends of the track core serve as end covers and a recirculation guide for the bearing rollers. Such roller track assemblies are described, for example, in the sales catalog No. 304 of Industrie-Werke Schaefler INA-Walzlager, 8522 Herzogenaurach, Germany.